Introduction
Supramolecular chemistry is one of the domain of chemistry focusing on entities of greater complexity than individual molecules-assemblies of molecules that bond and organize through intermolecular interactions. The design and synthesis of supramolecular systems invokes interactions beyond the covalent bond, using, for example, hydrogen bonding, metal coordination, van der Waals forces, electrostatic effects and π interactions to bring separated building blocks together. [1, 2]
Since introduction in 1985 by Tomalia et al., Newkome et al. and Vogtle et al., dendrimers, also known as arborols, or cascade, cauliflower, or starburst polymers are attracting increasing attention because of their unique structures and fascinating properties (e.g. monodisperzity, size, shape, biocompatibility, immunogenicity etc.) [3, 4, 5]. Dendrimers have a tremendous potential in creating new opportunities in medicine, biology, chemistry and many other fields.
This paper is about dendrimers in supramolecular chemistry and briefly describe host-guest interaction, self-assembly and self-organization along with active and passive targeting of dendrimers.
1. Host-Guest
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[3, 6] The first one is to constructed dendrons with a core unit that is able to recognize itself or a ditopic or polytopic core structure, which leads to spontaneous formation of a dendrimer. [3, 6, 12] The second approach is adding layers or generations to the peripheral groups by non-covalent binding. The both methods mentioned above are similar to convergent and divergent dendrimer synthesis. [6, 7] The third strategy is that dendrimers might be self-assembled by adding layers or generations through recognition units on the branched monomers inside the dendrimer.
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...Coauthor, ChemBioChem 2006, 7, 1-10; b) A. Author, B. Coauthor, Angew. Chem. 2006, 118, 1-5; Angew. Chem. Int. Ed. 2006, 45, 1-5.))
There are two types of synthetic polymers which are called condensation and addition polymers. The condensation polymers result when there is a reaction between two poly functional molecules which gets rid off a small molecule. For example, the polyester Dacron is a synthetic condensation polymer. Addition polymers on the other hand are formed in a domino effect including monomers with double bonds. Once the polymers are formed they tend to take on a linear shape or a star/comb like shape and then they are classified as linear and branched polymers. There are four major biological macromolecules which are carbohydrates, lipids, proteins and nucleic acids. Carbohydrates are sugar molecules that are made from C, H and O in a 1:2:1 ratio. Monosaccharides and disaccharides are carbohydrates divided into simple sugars while polysaccharides are carbohydrates that are divided into complex sugars such as starch. Lipids are substances like fat and phospholipids are important components of all living creatures. They are hydrophobic and thus it is difficult to break down to form energy. Biological polymers are made of amino acids, nucleotides and sugars. A significant biological polymer
SN2 reactions are described as bimolecular nucleophilic substitution reactions that occur in one concerted step without the formation of a carbocation intermediate. These reactions are performed most effectively in polar aprotic solvents such as acetone. The steric hindrance presented in the substrate is considered the most important factor due to the fact that the more steric hindrance there is around the halide, the harder it is for it to leave. The collected data for the SN2 reactions support this logic by showing that primary halides on substrates 4, 6, and 7 occurred within the first 5 minutes of the reaction. Substrates 6 and 7 were acted on immediately because 6 is allylic and 7 is benzylic, which creates an over lap of the pi bonds
The purpose of this experiment was to create a polymer by reacting a mixture of decanedioyl dichloride and dichloromethane with a mixture of water, 1,6-hexadiamine and sodium carbonate. Specifically, we created the polymer Nylon-6,10. Nylon-6,10 polymers are used in a vast majority of things we use in everyday life such as zippers, the bristles in brushes, and even car parts. This experiment was different from the industrial method of making nylon because that takes place at a much higher temperature. A polymer is a substance that has a structure made of similar or identical units bonded together. All polymerizations fall into two categories: step-growth and chain-growth (both of which we used to form our polymer). Step growth polymerization
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German Chemist Hans von Pechmann first synthesized Polyethylene by accident in 1898 by heating diazomethane. His colleagues characterized the waxy substance polyethylene due to the fact that they recognized that it consisted of long ethene chains. It was then first industrially synthesized by accident in 1933 by applying extremely high pressure to ethylene and benzaldehyde. Over the years, development of polyethylene has increased due to the additions of catalyst. This makes ethylene polymerization possible at lower temperatures and pressures.1
Azo compounds are those having R-N=N-R΄ functional group, where R and R΄ can be either aryl or alkyl. It is a derivative of Diazene (Diimide) NH=NH, where both the hydrogen replaced by hydrocarbonyl group e.g PhN=NPh (Azobenzene or diphenyldiazene). The N=N is called as azo group. As a consequence of π – delocalization phenyl azo compounds have vivid colour like red, yellow and orange, due to this, it is used as a dye and known as azo dye [3]. Azo compounds have been incorporated into a wide variety of materials and molecular architectures, dendrimers, polymers and molecular glasses. Due to clean and efficient photochemical isomerisation and substantial change in material properties during light irradiation it has been investigated as an active
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Ionic compounds, when in the solid state, can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible. Though there is some structural diversity in ionic compounds, covalent compounds present us with a world of structural possibilities. From simple linear molecules like H2 to complex chains of atoms like butane (CH3CH2CH2CH3), covalent molecules can take on many shapes. To help decide which shape a polyatomic molecule might prefer we will use Valence Shell Electron Pair Repulsion theory (VSEPR). VSEPR states that electrons like to stay as far away from one another as possible to provide the lowest energy (i.e. most stable) structure for any bonding arrangement. In this way, VSEPR is a powerful tool for predicting the geometries of covalent molecules.